1. Field of the Invention
This invention relates to a trimming device for a marine propulsion unit and more particularly to an improved connection between the trimming device and the propulsion unit.
2. Description of Related Art
In a wide variety of outboard drives, both outboard motors and the outboard drive section of an inboard/outboard drive, there is an arrangement incorporated for adjusting the trim position of the pivotally supported outboard drive. In one form of powered trim adjustment, a trim cylinder is carried by the transom of the watercraft and has an actuating rod or thrust member that engages the outboard drive and which urges it about its pivotal axis to change the trim position. In addition, the thrust member of the trim unit takes the driving thrust from the outboard drive during forward propulsion. Normally, the thrust member reciprocates along a fixed axis whereby the outboard drive pivots about a fixed axis. As a result of this, there will be relative movement between the thrust member and the outboard drive that can cause noise during operation. In addition, such relative movement results in wear, galling and other unsatisfactory conditions.
FIG. 1 illustrates the interaction between the thrust member and the outboard drive to further explain the disadvantages associated with prior trim adjust mechanisms. In particular, FIG. 1 illustrates, in isolation, thrust member (trim piston rod) 1 that reciprocates along a fixed axis 2, while a thrust taking member 3 is affixed to a front 4 of a swivel bracket along a fixed axis 5. The swivel bracket is a part of an outboard drive and will be described later. The axes 2, 5 are skewed relative to each other and an angle defined between the axes 2, 5 varies with the reciprocation of the thrust member 1. Accordingly, a contact point of the thrust member 1 with the thrust taking member 3 gradually shift. Because of this, the thrust member 1 generally has a round convex surface 6 at the end portion thereof and the thrust taking member 3 has a round concave surface 7 that cooperates with the convex surface 6 of the thrust member 1. Due to the skewed orientation of the axes 2, 5, a couple of components Fx and Fy of the force F occur. The force component Fx, in particular, becomes larger along with the expansion of the thrust member 1 and when the thrust member 1 is fully extended, that is, when the outboard drive is lifted to the uppermost position, the force component Fx also reaches its maximum. The force component Fx works to bend the thrust member 1. While the degree of deflection of the thrust member 1 may be slight and not damage the thrust member 1 because of its stiffness, such deflection can cause noise and other disadvantages, as noted above.
One way to avoid such disadvantages would be to incorporate a grease fitting. However, this requires servicing and posses the potential of dirtying an operator's hands and clothes. In addition, the grease may be depleted and if not promptly replaced, the same disadvantages can result again.
In order to resolve these problems, some attempts were made as disclosed in U.S. Pat. Nos. 4,720,278 and 4,764,134. These inventions, however, require somewhat complicated structures and hence tend to invite frequent exchanges of parts or components.